diff --git a/egui/benches/benchmark.rs b/egui/benches/benchmark.rs
index 0d828f45..0792b990 100644
--- a/egui/benches/benchmark.rs
+++ b/egui/benches/benchmark.rs
@@ -2,7 +2,7 @@ use criterion::{criterion_group, criterion_main, Criterion};
 
 pub fn criterion_benchmark(c: &mut Criterion) {
     let mut example_app = egui::examples::ExampleApp::default();
-    let mut ctx = egui::Context::new(1.0);
+    let mut ctx = egui::Context::new();
 
     let raw_input = egui::RawInput {
         screen_size: egui::vec2(1280.0, 1024.0),
@@ -11,8 +11,7 @@ pub fn criterion_benchmark(c: &mut Criterion) {
 
     c.bench_function("example_app", |b| {
         b.iter(|| {
-            ctx.begin_frame(raw_input.clone());
-            let mut ui = ctx.fullscreen_ui();
+            let mut ui = ctx.begin_frame(raw_input.clone());
             example_app.ui(&mut ui, "");
             ctx.end_frame()
         })
diff --git a/egui/src/context.rs b/egui/src/context.rs
index 867c1314..4dd93df8 100644
--- a/egui/src/context.rs
+++ b/egui/src/context.rs
@@ -16,13 +16,14 @@ struct PaintStats {
 /// `Ui`:s keep an Arc pointer to this.
 /// This allows us to create several child `Ui`:s at once,
 /// all working against the same shared Context.
+#[derive(Default)]
 pub struct Context {
     /// The default style for new `Ui`:s
     style: Mutex<Style>,
     paint_options: Mutex<paint::PaintOptions>,
-    fonts: Arc<Fonts>,
-    /// HACK: set a new font next frame
-    new_fonts: Mutex<Option<Arc<Fonts>>>,
+    /// None until first call to `begin_frame`.
+    fonts: Option<Arc<Fonts>>,
+    font_definitions: Mutex<FontDefinitions>,
     memory: Arc<Mutex<Memory>>,
 
     input: InputState,
@@ -42,7 +43,7 @@ impl Clone for Context {
             style: Mutex::new(self.style()),
             paint_options: Mutex::new(*self.paint_options.lock()),
             fonts: self.fonts.clone(),
-            new_fonts: Mutex::new(self.new_fonts.lock().clone()),
+            font_definitions: Mutex::new(self.font_definitions.lock().clone()),
             memory: self.memory.clone(),
             input: self.input.clone(),
             graphics: Mutex::new(self.graphics.lock().clone()),
@@ -54,21 +55,8 @@ impl Clone for Context {
 }
 
 impl Context {
-    pub fn new(pixels_per_point: f32) -> Arc<Context> {
-        Arc::new(Context {
-            style: Default::default(),
-            paint_options: Default::default(),
-            fonts: Arc::new(Fonts::new(pixels_per_point)),
-            new_fonts: Default::default(),
-            memory: Default::default(),
-
-            input: Default::default(),
-
-            graphics: Default::default(),
-            output: Default::default(),
-            used_ids: Default::default(),
-            paint_stats: Default::default(),
-        })
+    pub fn new() -> Arc<Self> {
+        Arc::new(Self::default())
     }
 
     pub fn rect(&self) -> Rect {
@@ -91,17 +79,25 @@ impl Context {
         &self.input
     }
 
+    /// Not valid until first call to `begin_frame()`
+    /// That's because since we don't know the proper `pixels_per_point` until then.
     pub fn fonts(&self) -> &Fonts {
-        &*self.fonts
+        &*self
+            .fonts
+            .as_ref()
+            .expect("No fonts available until first call to Contex::begin_frame()`")
     }
 
+    /// Not valid until first call to `begin_frame()`
+    /// That's because since we don't know the proper `pixels_per_point` until then.
     pub fn texture(&self) -> &paint::Texture {
         self.fonts().texture()
     }
 
-    /// Will become active next frame
-    pub fn set_fonts(&self, fonts: Fonts) {
-        *self.new_fonts.lock() = Some(Arc::new(fonts));
+    /// Will become active at the start of the next frame.
+    /// `pixels_per_point` will be ignored (overwitten at start of each frame with the contents of input)
+    pub fn set_fonts(&self, font_definitions: FontDefinitions) {
+        *self.font_definitions.lock() = font_definitions;
     }
 
     // TODO: return MutexGuard
@@ -139,10 +135,13 @@ impl Context {
 
     // ---------------------------------------------------------------------
 
-    pub fn begin_frame(self: &mut Arc<Self>, new_input: RawInput) {
+    /// Call at the start of every frame.
+    /// Returns a master fullscreen UI, covering the entire screen.
+    pub fn begin_frame(self: &mut Arc<Self>, new_input: RawInput) -> Ui {
         let mut self_: Self = (**self).clone();
         self_.begin_frame_mut(new_input);
         *self = Arc::new(self_);
+        self.fullscreen_ui()
     }
 
     fn begin_frame_mut(&mut self, new_raw_input: RawInput) {
@@ -150,13 +149,19 @@ impl Context {
 
         self.used_ids.lock().clear();
 
-        if let Some(new_fonts) = self.new_fonts.lock().take() {
-            self.fonts = new_fonts;
-        }
-
         self.input = std::mem::take(&mut self.input).begin_frame(new_raw_input);
+
+        let mut font_definitions = self.font_definitions.lock();
+        font_definitions.pixels_per_point = self.input.pixels_per_point;
+        if self.fonts.is_none() || *self.fonts.as_ref().unwrap().definitions() != *font_definitions
+        {
+            self.fonts = Some(Arc::new(Fonts::from_definitions(font_definitions.clone())));
+        }
     }
 
+    /// Call at the end of each frame.
+    /// Returns what has happened this frame (`Output`) as well as what you need to paint.
+    #[must_use]
     pub fn end_frame(&self) -> (Output, PaintBatches) {
         self.memory().end_frame();
         let output: Output = std::mem::take(&mut self.output());
@@ -195,7 +200,7 @@ impl Context {
     // ---------------------------------------------------------------------
 
     /// A `Ui` for the entire screen, behind any windows.
-    pub fn fullscreen_ui(self: &Arc<Self>) -> Ui {
+    fn fullscreen_ui(self: &Arc<Self>) -> Ui {
         let rect = Rect::from_min_size(Default::default(), self.input().screen_size);
         let id = Id::background();
         let layer = Layer {
@@ -365,7 +370,7 @@ impl Context {
         let align = (Align::Min, Align::Min);
         let layer = Layer::debug();
         let text_style = TextStyle::Monospace;
-        let font = &self.fonts[text_style];
+        let font = &self.fonts()[text_style];
         let galley = font.layout_multiline(text, f32::INFINITY);
         let rect = align_rect(Rect::from_min_size(pos, galley.size), align);
         self.add_paint_cmd(
@@ -422,7 +427,7 @@ impl Context {
         align: (Align, Align),
         text_color: Option<Color>,
     ) -> Rect {
-        let font = &self.fonts[text_style];
+        let font = &self.fonts()[text_style];
         let galley = font.layout_multiline(text, f32::INFINITY);
         let rect = align_rect(Rect::from_min_size(pos, galley.size), align);
         self.add_galley(layer, rect.min, galley, text_style, text_color);
@@ -471,17 +476,10 @@ impl Context {
         CollapsingHeader::new("Fonts")
             .default_open(false)
             .show(ui, |ui| {
-                let old_font_definitions = self.fonts().definitions();
-                let mut new_font_definitions = old_font_definitions.clone();
-                font_definitions_ui(&mut new_font_definitions, ui);
+                let mut font_definitions = self.fonts().definitions().clone();
+                font_definitions.ui(ui);
                 self.fonts().texture().ui(ui);
-                if *old_font_definitions != new_font_definitions {
-                    let fonts = Fonts::from_definitions(
-                        new_font_definitions,
-                        self.input().pixels_per_point,
-                    );
-                    self.set_fonts(fonts);
-                }
+                self.set_fonts(font_definitions);
             });
     }
 
@@ -564,21 +562,6 @@ impl Context {
     }
 }
 
-fn font_definitions_ui(font_definitions: &mut paint::FontDefinitions, ui: &mut Ui) {
-    use crate::widgets::*;
-    for (text_style, (_family, size)) in font_definitions.iter_mut() {
-        // TODO: radiobutton for family
-        ui.add(
-            Slider::f32(size, 4.0..=40.0)
-                .precision(0)
-                .text(format!("{:?}", text_style)),
-        );
-    }
-    if ui.add(Button::new("Reset fonts")).clicked {
-        *font_definitions = paint::fonts::default_font_definitions();
-    }
-}
-
 impl Context {
     pub fn style_ui(&self, ui: &mut Ui) {
         let mut style = self.style();
diff --git a/egui/src/introspection.rs b/egui/src/introspection.rs
index 448827bb..5641a372 100644
--- a/egui/src/introspection.rs
+++ b/egui/src/introspection.rs
@@ -1,13 +1,13 @@
 //! uis for egui types.
 use crate::{
     containers::show_tooltip,
-    label,
     math::*,
-    paint::{color::WHITE, PaintCmd, Texture, Triangles, Vertex},
+    paint::{self, color::WHITE, PaintCmd, Texture, Triangles, Vertex},
+    *,
 };
 
 impl Texture {
-    pub fn ui(&self, ui: &mut crate::Ui) {
+    pub fn ui(&self, ui: &mut Ui) {
         ui.add(label!(
             "Texture size: {} x {} (hover to zoom)",
             self.width,
@@ -60,3 +60,19 @@ impl Texture {
         }
     }
 }
+
+impl paint::FontDefinitions {
+    pub fn ui(&mut self, ui: &mut Ui) {
+        for (text_style, (_family, size)) in self.fonts.iter_mut() {
+            // TODO: radiobutton for family
+            ui.add(
+                Slider::f32(size, 4.0..=40.0)
+                    .precision(0)
+                    .text(format!("{:?}", text_style)),
+            );
+        }
+        if ui.add(Button::new("Reset fonts")).clicked {
+            *self = paint::FontDefinitions::with_pixels_per_point(self.pixels_per_point);
+        }
+    }
+}
diff --git a/egui/src/paint/fonts.rs b/egui/src/paint/fonts.rs
index 7115045b..80784a21 100644
--- a/egui/src/paint/fonts.rs
+++ b/egui/src/paint/fonts.rs
@@ -28,37 +28,47 @@ pub enum FontFamily {
     VariableWidth,
 }
 
-pub type FontDefinitions = BTreeMap<TextStyle, (FontFamily, f32)>;
+#[derive(Clone, Debug, PartialEq)]
+pub struct FontDefinitions {
+    /// The dpi scale factor. Needed to get pixel perfect fonts.
+    pub pixels_per_point: f32,
 
-pub fn default_font_definitions() -> FontDefinitions {
-    let mut definitions = FontDefinitions::new();
-    definitions.insert(TextStyle::Body, (FontFamily::VariableWidth, 14.0));
-    definitions.insert(TextStyle::Button, (FontFamily::VariableWidth, 16.0));
-    definitions.insert(TextStyle::Heading, (FontFamily::VariableWidth, 24.0));
-    definitions.insert(TextStyle::Monospace, (FontFamily::Monospace, 13.0));
-    definitions
+    pub fonts: BTreeMap<TextStyle, (FontFamily, f32)>,
 }
 
+impl Default for FontDefinitions {
+    fn default() -> Self {
+        Self::with_pixels_per_point(f32::NAN) // must be set later
+    }
+}
+
+impl FontDefinitions {
+    pub fn with_pixels_per_point(pixels_per_point: f32) -> Self {
+        let mut fonts = BTreeMap::new();
+        fonts.insert(TextStyle::Body, (FontFamily::VariableWidth, 14.0));
+        fonts.insert(TextStyle::Button, (FontFamily::VariableWidth, 16.0));
+        fonts.insert(TextStyle::Heading, (FontFamily::VariableWidth, 24.0));
+        fonts.insert(TextStyle::Monospace, (FontFamily::Monospace, 13.0));
+
+        Self {
+            pixels_per_point,
+            fonts,
+        }
+    }
+}
+
+/// Note: the `default()` fonts are invalid (missing `pixels_per_point`).
+#[derive(Default)]
 pub struct Fonts {
-    pixels_per_point: f32,
     definitions: FontDefinitions,
     fonts: BTreeMap<TextStyle, Font>,
     texture: Texture,
 }
 
 impl Fonts {
-    pub fn new(pixels_per_point: f32) -> Fonts {
-        Fonts::from_definitions(default_font_definitions(), pixels_per_point)
-    }
-
-    pub fn from_definitions(definitions: FontDefinitions, pixels_per_point: f32) -> Fonts {
-        let mut fonts = Fonts {
-            pixels_per_point,
-            definitions: Default::default(),
-            fonts: Default::default(),
-            texture: Default::default(),
-        };
-        fonts.set_sizes(definitions);
+    pub fn from_definitions(definitions: FontDefinitions) -> Fonts {
+        let mut fonts = Self::default();
+        fonts.set_definitions(definitions);
         fonts
     }
 
@@ -66,7 +76,7 @@ impl Fonts {
         &self.definitions
     }
 
-    pub fn set_sizes(&mut self, definitions: FontDefinitions) {
+    pub fn set_definitions(&mut self, definitions: FontDefinitions) {
         if self.definitions == definitions {
             return;
         }
@@ -93,7 +103,11 @@ impl Fonts {
         // let variable_typeface_data = include_bytes!("../../fonts/DejaVuSans.ttf"); // Basic, boring, takes up more space
 
         self.definitions = definitions.clone();
-        self.fonts = definitions
+        let FontDefinitions {
+            pixels_per_point,
+            fonts,
+        } = definitions;
+        self.fonts = fonts
             .into_iter()
             .map(|(text_style, (family, size))| {
                 let typeface_data: &[u8] = match family {
@@ -103,7 +117,7 @@ impl Fonts {
 
                 (
                     text_style,
-                    Font::new(atlas.clone(), typeface_data, size, self.pixels_per_point),
+                    Font::new(atlas.clone(), typeface_data, size, pixels_per_point),
                 )
             })
             .collect();
diff --git a/egui_wasm/Cargo.toml b/egui_wasm/Cargo.toml
index 7910dcd2..c461020f 100644
--- a/egui_wasm/Cargo.toml
+++ b/egui_wasm/Cargo.toml
@@ -14,7 +14,7 @@ serde = "1"
 serde_json = "1"
 wasm-bindgen = "0.2"
 
-egui = { path = "../egui" }
+egui = { path = "../egui", features = ["with_serde"] }
 
 [dependencies.web-sys]
 version = "0.3"
diff --git a/example_glium/src/main.rs b/example_glium/src/main.rs
index 02d80cf2..f12c87fb 100644
--- a/example_glium/src/main.rs
+++ b/example_glium/src/main.rs
@@ -50,7 +50,7 @@ fn main() {
     let context = glutin::ContextBuilder::new();
     let display = glium::Display::new(window, context, &events_loop).unwrap();
 
-    let size = window_settings.size.unwrap_or(vec2(1024.0, 800.0));
+    let size = window_settings.size.unwrap_or_else(|| vec2(1024.0, 800.0));
 
     display
         .gl_window()
@@ -67,7 +67,7 @@ fn main() {
 
     let pixels_per_point = display.gl_window().get_hidpi_factor() as f32;
 
-    let mut ctx = profile("initializing emilib", || Context::new(pixels_per_point));
+    let mut ctx = profile("initializing emilib", Context::new);
     let mut painter = profile("initializing painter", || {
         egui_glium::Painter::new(&display)
     });
@@ -111,8 +111,7 @@ fn main() {
         }
 
         let egui_start = Instant::now();
-        ctx.begin_frame(raw_input.clone()); // TODO: avoid clone
-        let mut ui = ctx.fullscreen_ui();
+        let mut ui = ctx.begin_frame(raw_input.clone()); // TODO: avoid clone
         example_app.ui(&mut ui, "");
         let mut ui = ui.centered_column(ui.available().width().min(480.0));
         ui.set_layout(Layout::vertical(Align::Min));
diff --git a/example_wasm/src/lib.rs b/example_wasm/src/lib.rs
index 2ac86e18..f1fd7663 100644
--- a/example_wasm/src/lib.rs
+++ b/example_wasm/src/lib.rs
@@ -38,8 +38,8 @@ pub struct State {
 }
 
 impl State {
-    fn new(canvas_id: &str, pixels_per_point: f32) -> Result<State, JsValue> {
-        let ctx = Context::new(pixels_per_point);
+    fn new(canvas_id: &str) -> Result<State, JsValue> {
+        let ctx = Context::new();
         egui_wasm::load_memory(&ctx);
         Ok(State {
             example_app: Default::default(),
@@ -52,9 +52,7 @@ impl State {
     fn run(&mut self, web_input: WebInput) -> Result<Output, JsValue> {
         let everything_start = now_sec();
 
-        self.ctx.begin_frame(web_input.egui);
-
-        let mut ui = self.ctx.fullscreen_ui();
+        let mut ui = self.ctx.begin_frame(web_input.egui);
         self.example_app.ui(&mut ui, &web_input.web.location_hash);
         let mut ui = ui.centered_column(ui.available().width().min(480.0));
         ui.set_layout(Layout::vertical(Align::Min));
@@ -111,8 +109,8 @@ impl State {
 }
 
 #[wasm_bindgen]
-pub fn new_webgl_gui(canvas_id: &str, pixels_per_point: f32) -> Result<State, JsValue> {
-    State::new(canvas_id, pixels_per_point)
+pub fn new_webgl_gui(canvas_id: &str) -> Result<State, JsValue> {
+    State::new(canvas_id)
 }
 
 #[wasm_bindgen]